U.S. patent application number 12/678412 was filed with the patent office on 2010-10-14 for plasma display panel.
This patent application is currently assigned to PANASONIC CORPORATION. Invention is credited to Osamu Inoue, Yayoi Okui, Kojiro Okuyama, Seigo Shiraishi.
Application Number | 20100259158 12/678412 |
Document ID | / |
Family ID | 41570167 |
Filed Date | 2010-10-14 |
United States Patent
Application |
20100259158 |
Kind Code |
A1 |
Okui; Yayoi ; et
al. |
October 14, 2010 |
PLASMA DISPLAY PANEL
Abstract
A plasma display panel (200) of the present invention includes a
first panel (1) and a second panel (8). A discharge space (14) is
formed between the first panel (1) and the second panel (8). In the
plasma display panel (200), an electron emitting material (20) is
disposed to face the discharge space (14). The electron emitting
material (20) contains Sn, an alkali metal, O (oxygen), and at
least one element selected from the group consisting of Ca, Sr, and
Ba.
Inventors: |
Okui; Yayoi; (Osaka, JP)
; Inoue; Osamu; (Osaka, JP) ; Okuyama; Kojiro;
(Nara, JP) ; Shiraishi; Seigo; (Osaka,
JP) |
Correspondence
Address: |
HAMRE, SCHUMANN, MUELLER & LARSON P.C.
P.O. BOX 2902
MINNEAPOLIS
MN
55402-0902
US
|
Assignee: |
PANASONIC CORPORATION
Kadoma-shi, Osaka
JP
|
Family ID: |
41570167 |
Appl. No.: |
12/678412 |
Filed: |
July 22, 2009 |
PCT Filed: |
July 22, 2009 |
PCT NO: |
PCT/JP2009/003446 |
371 Date: |
March 16, 2010 |
Current U.S.
Class: |
313/489 ;
313/491; 313/582 |
Current CPC
Class: |
H01J 11/12 20130101;
H01J 11/40 20130101 |
Class at
Publication: |
313/489 ;
313/582; 313/491 |
International
Class: |
H01J 17/49 20060101
H01J017/49; H01J 61/42 20060101 H01J061/42 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 25, 2008 |
JP |
2008-192602 |
Claims
1. A plasma display panel comprising a first panel and a second
panel with a discharge space being formed between the first panel
and the second panel, wherein an electron emitting material is
disposed to face the discharge space, and the electron emitting
material contains Sn, an alkali metal, O (oxygen), and at least one
element selected from the group consisting of Ca, Sr, and Ba.
2. The plasma display panel according to claim 1, wherein the
electron emitting material is represented by the general formula
a(M.sup.1O).SnO.sub.2.b(M.sup.2O.sub.0.5), where M.sup.1 is at
least one element selected from the group consisting of Ca, Sr, and
Ba, M.sup.2 is at least one element selected from the group
consisting of Li, Na, K, Rb, and Cs, a value of a is in a range of
1 or more to 2 or less, and a value of b is in a range of 0.002 or
more to 0.3 or less.
3. The plasma display panel according to claim 1, wherein the first
panel includes a first substrate, a first electrode formed on the
first substrate, and a first dielectric layer formed to cover the
first electrode, the second panel includes a second substrate, a
second electrode formed on the second substrate, a second
dielectric layer formed to cover the second electrode, and a
phosphor layer, and the electron emitting material is disposed on
at least one panel selected from the first panel and the second
panel so as to face the discharge space.
4. The plasma display panel according to claim 3, wherein the
electron emitting material is disposed in at least one form
selected from particles and a film.
5. The plasma display panel according to claim 3, wherein a
protective layer is formed on the first dielectric layer.
6. The plasma display panel according to claim 5, wherein the
protective layer is made of MgO.
7. The plasma display panel according to claim 5, wherein the
electron emitting material is disposed on the protective layer in
at least one form selected from particles and a film.
8. The plasma display panel according to claim 5, wherein the
protective layer includes the electron emitting material.
9. The plasma display panel according to claim 2, wherein the first
panel includes a first substrate, a first electrode formed on the
first substrate, and a first dielectric layer formed to cover the
first electrode, the second panel includes a second substrate, a
second electrode formed on the second substrate, a second
dielectric layer formed to cover the second electrode, and a
phosphor layer, and the electron emitting material is disposed on
at least one panel selected from the first panel and the second
panel so as to face the discharge space.
10. The plasma display panel according to claim 9, wherein the
electron emitting material is disposed in at least one form
selected from particles and a film.
11. The plasma display panel according to claim 9, wherein a
protective layer is formed on the first dielectric layer.
12. The plasma display panel according to claim 11, wherein the
protective layer is made of MgO.
13. The plasma display panel according to claim 11, wherein the
electron emitting material is disposed on the protective layer in
at least one form selected from particles and a film.
14. The plasma display panel according to claim 11, wherein the
protective layer includes the electron emitting material.
Description
TECHNICAL FIELD
[0001] The present invention relates to plasma display panels.
BACKGROUND ART
[0002] Plasma display panels (hereinafter referred to as PDPs),
which are one type of flat panel display, have been developed for
practical use and have spread rapidly because of their advantages
such as easy upsizing, high-speed display, and low cost.
[0003] A commercially available common PDP has a structure in which
two glass substrates facing each other, which serve as a front
substrate and a rear substrate, each have regularly arranged
electrodes and a dielectric layer made of low-melting glass or the
like to cover these electrodes. On the dielectric layer of the rear
substrate, phosphor layers are provided. On the dielectric layer of
the front substrate, a MgO layer as a protective layer is provided
to protect the dielectric layer from ion bombardment and to cause
secondary electrons to be emitted. A gas containing an inert gas
such as Ne or Xe as a main component is sealed into the space
between the two substrates and a voltage is applied between the
electrodes to generate a discharge, thus causing the phosphors to
emit light so that an image is displayed.
[0004] There has been a strong demand for high efficiency PDPs. In
order to meet this demand, there have been known a method of
reducing the dielectric constant of a dielectric layer and a method
of increasing the partial pressure of Xe in a discharge gas. The
use of these methods, however, causes a problem that a firing
potential and a sustaining voltage increase.
[0005] It has been known that if a protective layer is made of a
material having a high secondary electron emission coefficient, the
firing potential and sustaining voltage can be reduced. In this
case, a high efficiency PDP can be obtained at low cost because
elements having low withstand voltages can be used. For this
purpose, it has been considered to use CaO, SrO or BaO, or a solid
solution of these oxides instead of MgO, because each of these
oxides has a higher secondary electron emission coefficient than
MgO even though it also is an alkaline earth metal oxide (Patent
Literatures 1 and 2).
CITATION LIST
Patent Literature
[0006] Patent Literature 1: JP 52 (1977)-63663 A
[0007] Patent Literature 2: JP 2007-95436 A
SUMMARY OF INVENTION
Technical Problem
[0008] Since CaO, SrO and BaO are, however, chemically unstable
compared with MgO, they react easily with moisture and carbon
dioxide in the air to form hydroxides and carbonates respectively.
When these hydroxides and carbonates are formed, the following
problems occur. That is, the secondary electron emission
coefficient decreases and the voltages cannot be reduced as
expected, or the aging process of the resulting PDP, which is
considered necessary to reduce the voltages, takes a very long time
and its practicality is reduced.
[0009] Such a deterioration caused by a chemical reaction can be
avoided by, for example, controlling the atmospheric gas used in
the manufacturing process, if a small number of PDPs are produced
in a laboratory. It is, however, difficult to control the
atmosphere throughout the production processes in a factory, and
the production cost would increase, even if possible. Therefore,
only MgO has still been used practically even though the use of
materials having higher secondary electron emission coefficients
has been considered conventionally. As a result, a sufficiently
high efficiency PDP driven at a sufficiently low voltage has not
yet been obtained.
[0010] Accordingly, it is an object of the present invention to
provide a PDP having a low driving voltage by improving the
discharge characteristics of the PDP by using an electron emitting
material having an excellent chemical stability and a high
secondary electron emission coefficient.
Solution of Problem
[0011] The present invention provides a PDP including a first panel
and a second panel with a discharge space being formed between the
first panel and the second panel. In this PDP, an electron emitting
material is disposed to face the discharge space, and the electron
emitting material contains Sn, an alkali metal, O (oxygen), and at
least one element selected from the group consisting of Ca, Sr, and
Ba.
ADVANTAGEOUS EFFECTS OF INVENTION
[0012] According to the present invention, it is possible to
provide a PDP having a low driving voltage by using a chemically
stable electron emitting material having a high secondary electron
emission coefficient.
BRIEF DESCRIPTION OF DRAWINGS
[0013] FIG. 1 is an exploded perspective diagram for explaining an
example of a PDP of the present invention.
[0014] FIG. 2 is a longitudinal sectional view of the PDP shown in
FIG. 1.
[0015] FIG. 3 is an exploded perspective diagram for explaining
another example of a PDP of the present invention.
[0016] FIG. 4 is a longitudinal sectional view of the PDP shown in
FIG. 3.
DESCRIPTION OF EMBODIMENT
[0017] As a result of detailed studies, the present inventors have
found that a material containing Sn, an alkali metal, O, and at
least one element selected from the group consisting of Ca, Sr, and
Ba, that is, a material obtained by reacting SnO.sub.2 and an
alkali metal with CaO, SrO, and/or BaO, has an excellent chemical
stability and has a higher secondary electron emission coefficient
than that of MgO that has been used conventionally as an electron
emitting material, even though CaO, SrO and BaO themselves are
chemically unstable even though they have high secondary electron
emission coefficients. As a result, the present inventors have
found that the use of such a material as an electron emitting
material of a PDP allows the driving voltage of the PDP to be
reduced compared with the use of conventional MgO.
[0018] A compound produced by combining chemically unstable CaO,
SrO, and/or BaO with SnO.sub.2 overcomes the chemical instability
of CaO, SrO, and BaO effectively, and particularly inhibits the
hydroxylation thereof effectively. The further addition of an
alkali metal to such a material containing SnO.sub.2 and CaO, SrO,
and/or BaO particularly inhibits the carbonation of CaO, SrO, and
BaO effectively. As described above, an electron emitting material
having a high secondary electron emission coefficient and an
excellent chemical stability with inhibited hydroxylation and
carbonation can be obtained by combining Sn, an alkali metal, O,
with at least one element selected from the group consisting of Ca,
Sr, and Ba. Such a material has high electron emission performance
and the electron emission performance does not degrade easily.
Therefore, when such a material is used as an electron emitting
material of a PDP, the PDP has a low driving voltage and has a good
stability.
[0019] In order to achieve more reliably the excellent chemical
stability and the higher secondary electron emission coefficient
than that of MgO that has been used conventionally as an electron
emitting material, it is preferable that the electron emitting
material used in the present invention contains, as a main
component, Sn, an alkali metal, O, and at least one element
selected from the group consisting of Ca, Sr, and Ba. As used
herein, the phrase "the electron emitting material contains, as a
main component, Sn, an alkali metal, O, and at least one element
selected from the group consisting of Ca, Sr, and Ba" means that
the total content of Sn, the alkali metal, and at least one element
selected from the group consisting of Ca, Sr, and Ba is at least 60
atomic %, preferably at least 90 atomic %, relative to the total
content of cations in the electron emitting material, although the
preferable content of these elements cannot be determined
definitely because it depends on the properties of the other
elements.
[0020] The structure of the electron emitting material used in the
present invention is not particularly limited as long as it is a
material containing Sn, an alkali metal, O, and at least one
element selected from the group consisting of Ca, Sr, and Ba. For
example, it may have a crystalline structure, or may be in an
amorphous state. The electron emitting material may be a compound
in which Ca, Sr, and/or Ba, or Sn are substituted partially with
other elements. In this case, it is preferable that the amount of
partially-substituted elements is within the range satisfying the
above-mentioned total content of Sn, an alkali metal, O, and Ca,
Sr, and/or Ba. Further preferably, the amount of
partially-substituted elements is within a reasonable range in
which the properties required for the electron emitting material
used in the present invention (i.e., the properties of chemical
stability and high second electron emission efficiency) are not
impaired essentially.
[0021] In order to obtain more reliably the properties required for
the electron emitting material used in the present invention, it is
desirable that the electron emitting material used in the present
invention consist essentially of Sn, an alkali metal, O, and at
least one element selected from the group consisting of Ca, Sr,
and/or Ba. As used herein, the phrase "the electron emitting
material consists of Sn, an alkali metal, O, and at least one
element selected from the group consisting of Ca, Sr, and Ba" means
that the electron emitting material contains no other elements, or
even if it contains other elements, the content of the elements is
as low as that of inevitably contained impurities.
[0022] Preferably, the electron emitting material used in the
present invention is a material represented by the general formula
a(M.sup.1O).SnO.sub.2.b(M.sup.2O.sub.0.5) to achieve a higher
chemical stability. As described above, the structure of the
electron emitting material is not particularly limited, but it is
desirably a crystalline compound because the crystalline compound
exhibits a high chemical stability. In the above general formula,
M.sup.1 is at least one element selected from the group consisting
of Ca, Sr, and Ba, and M.sup.2 is at least one element selected
from the group consisting of Li, Na, K, Rb, and Cs. The value of a
is in the range of 1 or more to 2 or less, and the value of b is in
the range of 0.002 or more to 0.3 or less. Hereinafter, the letters
M.sup.1, M.sup.2, a, and b are used in the same sense as described
above.
[0023] As to the secondary electron emission coefficient, a
material containing SrO has a higher coefficient than that
containing CaO, and further a material containing BaO has a still
higher coefficient than that containing SrO. On the other hand, as
to the chemical stability, a material containing SrO has a higher
stability than that containing BaO, and further a material
containing CaO has a still higher stability than that containing
SrO.
[0024] Examples of the method of synthesizing an electron emitting
material containing Sn, an alkali metal, O, and at least one
element selected from Ca, Sr, and Ba include a solid phase method,
a liquid phase method, and a vapor phase method.
[0025] A solid phase method is a method in which powdered raw
materials containing the above-mentioned metal elements (such as
metal oxides and metal carbonates) are mixed and the mixture is
subjected to heat treatment at a certain temperature or higher for
the reaction thereof.
[0026] A liquid phase method is a method in which a solution
containing the above-mentioned metal elements is prepared and a
solid phase precipitated from the solution is obtained or the
solution is applied to a substrate, dried, and then subjected to
heat treatment or the like at a certain temperature or higher to
obtain a solid phase.
[0027] A vapor phase method is a method of obtaining a solid-phase
film by a technique such as vapor deposition, sputtering, or CVD.
In the vapor phase method, not only a crystalline oxide containing
Sn, an alkali metal, and Ca, Sr, and/or Ba at a specific ratio, but
also an amorphous compound containing Sn, an alkali metal, O, and
Ca, Sr, and/or Ba can be obtained. Such an amorphous compound also
is more chemically stable than CaO, SrO, or BaO, and has a higher
secondary electron emission coefficient than MgO. Therefore, the
use of such an amorphous compound reduces the driving voltage of
the PDP.
[0028] A crystalline material has, however, has a higher chemical
stability than an amorphous material. In addition, the vapor phase
method used as a synthesis method to obtain an amorphous compound
costs more than the solid phase method or the like. Therefore, the
electron emitting material used in the present invention preferably
is a crystalline compound.
[0029] In the PDP of the present invention, the electron emitting
material is disposed to face the discharge space. For example, the
electron emitting material can be disposed on at least one panel
selected from the first panel and the second panel of the PDP so as
to face the discharge space. Generally, any of these electron
emitting materials may be formed on the dielectric layer covering
the electrodes on the front panel. The electron emitting material
also may be formed on another portion of the PDP, for example, on
the phosphor or the surface of the barrier rib as long as the
portion faces the discharge space. In this case, a greater effect
of driving voltage reduction is seen than the case where no
electron emitting material is formed.
[0030] Next, examples of the form of the electron emitting material
provided in the PDP will be described. The electron emitting
material can be disposed in at least one form selected from
particles and a film. For example, in the case where the electron
emitting material is formed on the dielectric layer (first
dielectric layer) covering the electrodes on the front panel (first
panel), the following methods can be used: a method in which a film
of the electron emitting material is formed or a powder of the
electron emitting material is spread on the dielectric layer
instead of forming a conventional MgO film as a protective layer on
the dielectric layer; and a method in which a MgO film is formed
and then a film of the electron emitting material is formed or a
powder of the electron emitting material is spread on the MgO film.
When the electron emitting material is used in the form of powder,
the particle diameter may be selected from the range of
approximately 0.1 to 10 .mu.m according to the cell size or the
like.
[0031] In the present description, as an example of the electron
emitting material, a material represented by
a(M.sup.1O).SnO.sub.2.b(M.sup.2O.sub.0.5) is given. Sn is an
element that is converted to Sn.sup.4+ easily. A part of Sn,
however, is converted to Sn.sup.2+ easily. In this case, an oxygen
vacancy occurs. Therefore, the electron emitting material should be
represented by a(M.sup.1O).SnO.sub.2--.delta..b(M.sup.2O.sub.0.5)
more accurately. However, the value of .delta. is not constant
because it varies depending on the production conditions, etc.
Therefore, the electron emitting material herein is represented by
a(M.sup.1O).SnO.sub.2.b(M.sup.2O.sub.0.5), which is not meant to
preclude the presence of oxygen vacancy. That is, materials
represented by a(M.sup.1O).SnO.sub.2.b(M.sup.2O.sub.0.5) include a
compound in which an oxygen vacancy occurs. The oxygen vacancy
occurring inevitably during the production process does not have a
particularly significant effect on the properties of the electron
emitting material used in the present invention.
[0032] Tetravalent Sn can be substituted partially with another
tetravalent element such as Ti or Zr, a trivalent In, a pentavalent
Nb, or the like. Each of divalent Ca, Sr, and Ba also can be
substituted partially with another divalent element such as Mg, a
trivalent La, or the like. As described above, the above-mentioned
elements contained in the electron emitting material used in the
present invention may be substituted slightly as long as the
material contains Sn, an alkali metal, O, and at least one element
selected from the group consisting of Ca, Sr, and Ba (preferably,
the material contains these elements as a main component).
[0033] Next, specific examples of the PDP of the present invention
will be described with reference to the accompanying drawings. FIG.
1 and FIG. 2 each illustrate an example of the PDP according to the
present invention. FIG. 1 is an exploded perspective view of a PDP
100. FIG. 2 is a longitudinal sectional view of the PDP 100 (i.e.,
a cross-sectional view taken along a line I-I in FIG. 1). As shown
in FIGS. 1 and 2, the PDP 100 has a front panel (first panel) 1 and
a rear panel (second panel) 8. Discharge spaces 14 are formed
between the front panel 1 and the rear panel 8. This PDP 100 is of
an AC plane discharge type and has the same configuration as that
of a conventional PDP except that a protective layer 7 is formed of
the above-mentioned compound.
[0034] The front panel 1 includes: a front glass substrate (first
substrate) 2; display electrodes (first electrodes) 5, each of
which is composed of a transparent conductive film 3 and a bus
electrode 4, and is formed on the inner surface (the surface facing
the discharge space 14) of the front glass substrate 2; a
dielectric layer (first dielectric layer) 6 formed to cover the
display electrodes 5; and a protective layer 7 formed on the
dielectric layer 6. The display electrodes 5 each are formed with
the bus electrode 4 made of, for example, Ag, being stacked on the
transparent conductive film 3 made of ITO or tin oxide in order to
ensure good conductivity.
[0035] The rear panel 8 includes: a rear glass substrate (second
substrate).sub.9; address electrodes (second electrodes) 10 formed
on one surface of the rear glass substrate 9; a dielectric layer
(second dielectric layer) 11 formed to cover the address electrodes
10; barrier ribs 12 provided on the upper surface of the dielectric
layer 11; and phosphor layers formed between the adjacent barrier
ribs 12. The phosphor layers are formed so that a red phosphor
layer 13(R), a green phosphor layer 13(G), and a blue phosphor
layer 13(B) are arranged in this order.
[0036] For the phosphors that constitute the phosphor layers,
BaMgAl.sub.10O.sub.17:Eu can be used as a blue phosphor,
Zn.sub.2SiO.sub.4:Mn can be used as a green phosphor, and
Y.sub.2O.sub.3:Eu can be used as a red phosphor, for example.
[0037] The front panel 1 and the rear panel 8 are disposed so that
the display electrodes 5 and the address electrodes 10 are
orthogonal to each other in their longitudinal directions and they
oppose each other, and are joined with a sealing member (not
shown).
[0038] A discharge gas composed of a rare gas such as He, Xe or Ne
is sealed in the discharge space 14.
[0039] The display electrodes 5 and the address electrodes 10 each
are connected to an external drive circuit (not shown). When a
voltage is applied from the drive circuit, a discharge is generated
in the discharge space 14, and ultraviolet rays with a short
wavelength (a wavelength of 147 nm) are generated by the discharge.
The phosphor layers 13 are excited by the ultraviolet rays to emit
visible light. The above-mentioned electron emitting material is
used for the protective layer 7.
[0040] FIG. 3 and FIG. 4 each illustrate another example of the PDP
according to the present invention. FIG. 3 is an exploded
perspective view of the PDP 200. FIG. 4 is a longitudinal sectional
view of the PDP 200 (i.e., a cross-sectional view taken along a
line I-I in FIG. 3). The PDP 200 has the same configuration as that
of the PDP 100 except that the protective layer 7 is made of MgO
and the above-mentioned electron emitting material 20 is provided
in the form of particles on the protective layer 7. Also in the PDP
200, the electron emitting material 20 is disposed to face the
discharge space 14.
[0041] Next, a method of manufacturing the PDP 200 by spreading a
powder of the above-mentioned electron emitting material on the
protective layer 7 made of a conventional MgO film will be
described using an example. First, the front panel 1 is produced. A
plurality of linear transparent electrodes 3 are formed on one
principal surface of the flat front glass substrate 2.
Subsequently, a silver paste is applied onto the transparent
electrodes and then is baked by heating the whole front glass
substrate 1, and thereby bus electrodes 4 are formed. As a result,
the display electrodes 5 are formed.
[0042] A glass paste containing glass for the dielectric layer 6 of
the PDP 200 of the present embodiment is applied to the
above-mentioned principal surface of the front glass substrate 2 by
the blade coater method so as to cover the display electrodes 5.
Thereafter, the whole front glass substrate 2 is maintained at
90.degree. C. for 30 minutes and thereby the glass paste is dried.
Subsequently, it is baked at a temperature of around 580.degree. C.
for 10 minutes.
[0043] A film of magnesium oxide (MgO) is formed on the dielectric
layer 6 by an electron beam vapor deposition method and then is
baked at a temperature around 500.degree. C. Thus, the protective
layer 7 is formed.
[0044] A paste is prepared by mixing a vehicle such as ethyl
cellulose with the powdery electron emitting material used in the
present invention. The paste is applied to the protective layer 7
by a printing method or the like, dried, and then baked at a
temperature around 500.degree. C. Thus, a layer in which the
particles of the electron emitting material 20 are spread is
formed.
[0045] Next, the rear panel 8 is produced. After a silver paste is
applied to one principal surface of the flat rear glass substrate 9
in the form of a plurality of lines, the whole rear glass substrate
9 is heated and thereby the silver paste is baked. Thus the address
electrodes 10 are formed.
[0046] A glass paste is applied between adjacent address electrodes
10, and the glass paste is baked by heating the whole rear glass
substrate 9. Thus, barrier ribs 12 are formed.
[0047] Phosphor inks with respective R, G, and B colors are applied
between adjacent barrier ribs 12, the above-mentioned phosphor inks
are baked by heating the rear glass substrate 9 at 500.degree. C.,
and thereby a resin component (binder) in the phosphor inks is
removed. Thus, phosphor layers are formed.
[0048] The front panel 1 and the rear panel 8 thus obtained are
bonded to each other using sealing glass at a temperature around
500.degree. C. Then, the sealed inner space is subjected to high
vacuum evacuation, and then rare gas is sealed therein.
[0049] PDP 200 is obtained as described above.
[0050] The above-mentioned PDP and the method of producing it are
examples and the present invention is not limited thereto.
[0051] In the case where the protective layer 7 is formed by
providing the above-mentioned electron emitting material used in
the present invention as a thin film instead of forming the
protective layer 7 made of a MgO film, a conventional thin film
formation technique such as electron beam vapor deposition may be
used as in the case of the MgO film. Another method may be used. A
paste having a high content of the powdery electron emitting
material is prepared by mixing the powdery material with a vehicle,
a solvent, or the like. A thin coating of this paste is applied by
a printing method or the like, and then baked to obtain a thin film
or a thick film.
[0052] On the other hand, in the case where the powdery electron
emitting material is spread, a paste having a relatively low
content of the powdery material may be spread by a printing method,
a solvent in which the powdery material is dispersed may be spread,
or a spin coater method may be used.
Examples
[0053] Hereinafter, the present invention is described further in
detail with reference to Examples.
[0054] [Electron Emitting Materials]
[0055] In the examples below, the effect of reducing the carbonate
formation of the following materials is described: an electron
emitting material synthesized by reacting CaCO.sub.3 with SnO.sub.2
and K.sub.2CO.sub.3 by the solid phase method; an electron emitting
material synthesized by reacting SrCO.sub.3 with SnO.sub.2, and
Li.sub.2CO.sub.3, Na.sub.2CO.sub.3, or K.sub.2CO.sub.3 by the solid
phase method; and an electron emitting material synthesized by
reacting BaCO.sub.3 with SnO.sub.2, and Li.sub.2CO.sub.3,
Na.sub.2CO.sub.3, K.sub.2CO.sub.3, Rb.sub.2CO.sub.3, or
Cs.sub.2CO.sub.3 by the solid phase powder method.
[0056] As starting materials, CaCO.sub.3, SrCO.sub.3, BaCO.sub.3,
SnO.sub.2, Li.sub.2CO.sub.3, Na.sub.2CO.sub.3, K.sub.2CO.sub.3,
Rb.sub.2CO.sub.3, and Cs.sub.2CO.sub.3 of at least special grade
reagents were used. These materials were weighed according to the
molar ratios of respective metal ions shown in Table 1, wet-mixed
in a ball mill, and then dried. Thus, respective powder mixtures
were obtained.
[0057] These powder mixtures each were put into a platinum
crucible, and fired in air in an electric furnace at 1200 to
1500.degree. C. for 2 hours to obtain powder samples. The average
particle diameter of each powder sample was measured. The powder
samples consisting of large particles were pulverized in a wet type
ball mill using ethanol as a solvent. Thus, the average particle
diameters of all the powder samples having respective compositions
were adjusted to about 3 .mu.m.
[0058] Next, part of each pulverized powder sample was analyzed by
X-ray photoelectron spectroscopy (XPS) to obtain a narrow spectrum
of C1s. The intensity of the peak derived from carbonate groups in
the spectrum (i.e., the peak whose peak top is located around 288
to 290 eV) was integrated to calculate the degree of carbonation.
It means that in a compound as a powder sample having a lower
degree of carbonation, a smaller amount of carbonates is formed,
which imparts better chemical stability to the sample. For
comparison, the degree of carbonation of a MgO powder (Sample No.
24) also was measured in the same manner. Table 1 shows the degrees
of carbonation measured.
TABLE-US-00001 TABLE 1 General formula:
a(M.sup.1O).cndot.SnO.sub.2.cndot.b(M.sup.2O.sub.0.5) Examples
& Comparative Degree of No. (Com.) Examples M.sup.1 M.sup.2 a b
carbonation 1 Com. Example Ca K 1 0 516 2 Example K 1 0.05 135 3
Com. Example K 2 0 1664 4 Example K 2 0.05 953 5 Com. Example Sr K
1 0 754 6 Example K 1 0.05 164 7 Example K 1 0.002 382 8 Example K
1 0.3 358 9 Example Li 1 0.05 621 10 Example Na 1 0.05 482 11 Com.
Example Ba K 1 0 850 12 Example K 1 0.002 453 13 Example K 1 0.01
397 14 Example K 1 0.03 222 15 Example K 1 0.05 209 16 Example K 1
0.1 265 17 Example K 1 0.2 355 18 Example K 1 0.3 451 19 Example K
1 0.4 875 20 Example Li 1 0.05 642 21 Example Na 1 0.05 515 22
Example Rb 1 0.05 212 23 Example Cs 1 0.05 203 24 Reference (MgO)
-- -- -- -- 1011
[0059] The degrees of carbonation of respective samples obtained by
XPS were as follows. Samples No. 1, No. 5 and No. 11 containing no
alkali metal had smaller values than the value of Sample No. 24
(MgO). It was found that Samples No. 2, No. 6, and Nos. 12 to 18,
in which alkali metals were added to the compositions of Samples
No. 1, No. 5, and No. 11, respectively, had extremely low degrees
of carbonation compared with those of Samples No. 1, No. 5, and No.
11 of Comparative Examples containing no alkali metal. Accordingly,
it was confirmed that the addition of an alkali metal increased the
stabilization effect dramatically. It also was confirmed from the
degrees of carbonation of Samples Nos. 5 to 23 that a desirable
value of b is in the range of 0.002 or more to 0.3 or less. It
further was confirmed that any of the alkali metals, Li, Na, K, Rb,
and Cs, has the effect of suppressing the formation of
carbonates.
[0060] In the case of a compound represented by
a(M.sup.1O).SnO.sub.2.b(M.sup.2O.sub.0.5), the value of a basically
is 1, 1.5, or 2. As a result of the inventors' studies, however,
even a mixture containing two alkaline earth metals like, for
example, a mixture having an intermediate composition of
(Sr.sub.0.5Ba.sub.0.5).SnO.sub.2O.sub.2.0.05(KO.sub.0.5) between
those of Sample No. 6 and Sample No. 15, exhibited intermediate
properties between those of Sample No. 6 and Sample No. 15. Thus,
the stabilization effect was obtained. Presumably, the similar
stabilization effect can be obtained in a mixture containing at
least two alkaline earth metals at another ratio.
[0061] [PDP]
[0062] In the present examples, a PDP, to which the electron
emitting material with improved chemical stability used in the
present invention is applied, is shown. A flat front glass
substrate made of soda lime glass with a thickness of about 2.8 mm
was prepared. A material of ITO (transparent electrodes) was
applied in a predetermined pattern on the surface of the front
glass substrate, and then was dried. Subsequently, a silver paste,
which was a mixture of silver powder and organic vehicle, was
applied in the form of a plurality of lines. Thereafter, the whole
front glass substrate was heated and thereby the silver paste was
baked to form display electrodes.
[0063] The glass paste was applied to the front panel on which the
display electrodes had been produced, using the blade coater
method. The panel was maintained at 90.degree. C. for 30 minutes so
that the glass paste was dried, and then the glass paste was baked
at a temperature of 585.degree. C. for 10 minutes. Thus, a
dielectric layer with a thickness of about 30 .mu.m was formed.
[0064] Magnesium oxide (MgO) was vapor-deposited on the
above-described dielectric layer by the electron beam vapor
deposition method. Thereafter, it was baked at 500.degree. C. and
thereby a protective layer was formed.
[0065] About 3 parts by weight of each of the powder samples Nos.
11, 15, and 24 were mixed with 100 parts by weight of ethyl
cellulose vehicle, and the resulting mixture was kneaded with a
three roll mill to obtain a paste. A thin coating of this paste was
applied by the printing method on the protective layer (MgO layer),
dried at 90.degree. C., and then baked in air at 500.degree. C.
During this process, the density of the paste was adjusted so that
about 20% of the baked protective layer was coated with the powder.
For comparison, a panel, in which the paste printing was not
performed, (i.e., a panel, in which the electron emitting material
used in the present invention was not provided), also was
produced.
[0066] On the other hand, the rear panel was produced by the
following method.
[0067] First, address electrodes composed mainly of silver were
formed in the form of stripes on a rear glass substrate made of
soda lime glass, by screen printing. Subsequently, a dielectric
layer with a thickness of about 8 .mu.m was formed by the same
method as that used for forming the front panel.
[0068] Next, a glass paste was used to form barrier ribs between
adjacent address electrodes on the dielectric layer. The barrier
ribs were formed by repeating screen printing and baking.
[0069] Subsequently, phosphor pastes of red (R), green (G), and
blue (B) were applied to the wall surfaces of the barrier ribs and
the surface of the dielectric layer exposed between the barrier
ribs, and then were dried and baked to produce phosphor layers.
[0070] The front panel and rear panel thus produced were bonded to
each other at 500.degree. C. using a sealing glass. Then, the
discharge space was evacuated, and then filled with Xe as a
discharge gas and sealed. Thus a PDP was produced.
[0071] The panel thus obtained was connected to a driving circuit
to cause the panel to emit light. The discharge sustaining voltage
of the panel in which MgO powder of Sample No. 24 was spread was
reduced by 6% with respect to that of the panel in which the
electron emitting material used in the present invention was not
provided. In contrast, the discharge sustaining voltages of the
panels in which the powders of Samples No. 11 and No. 15 were
spread were reduced by 17% and 20% respectively. It was confirmed
from these results that the discharge sustaining voltage can be
reduced by disposing the electron emitting material containing Sn,
an alkali metal, O, and at least one element selected from the
group consisting of Ca, Sr, and Ba to face the discharge space, as
in the PDP of the present invention.
INDUSTRIAL APPLICABILITY
[0072] The present invention can be applied suitably to PDPs that
require a further reduction in voltage consumption.
* * * * *